The present invention relates to cochlear implants, and more particularly to a method for sensing, measuring and using the stapedial reflex in a cochlear implant through the use of multiband stimuli.
Electrical stimulation of predetermined locations within the cochlea of the human ear through an intra-cochlear electrode array is described, e.g., in U.S. Pat. No. 4,400,590. The electrode array shown in the '590 patent comprises a plurality of exposed electrode pairs spaced along and imbedded in a resilient curved base for implantation in accordance with a method of surgical implantation, e.g., as described in U.S. Pat. No. 3,751,615. The system described in the '590 patent receives audio signals, i.e., sound waves, at a signal processor (or speech processor) located outside the body of a hearing impaired patient. The speech processor converts the received audio signals into modulated RF data signals that are transmitted by a cable connection through the patient's skin to an implanted multi-channel intracochlear electrode array. The modulated RF signals are demodulated into analog signals and are applied to selected ones of the plurality of exposed electrode pairs in the intra-cochlear electrode so as to electrically stimulate predetermined locations of the auditory nerve within the cochlea.
U.S. Pat. No. 5,938,691, incorporated herein by reference, shows an improved multi-channel cochlear stimulation system employing an implanted cochlear stimulator (ICS) and an externally wearable speech processor (SP). The speech processor employs a headpiece that is placed adjacent to the ear of the patient, which receives audio signals and transmits the audio signals back to the speech processor. The speech processor receives and processes the audio signals and generates data indicative of the audio signals for transcutaneous transmission to the implantable cochlear stimulator. The implantable cochlear stimulator receives the transmission from the speech processor and applies stimulation signals to a plurality of cochlea stimulating channels, each having a pair of electrodes in an electrode array associated therewith. Each of the cochlea stimulating channels uses a capacitor to couple the electrodes of the electrode array.
Other improved features of a cochlear implant system are taught, e.g., in U.S. Pat. Nos. 5,626,629; 6,067,474; 6,157,861; 6,195,585; 6,205,360; 6,219,580; 6,249,704; 6,289,247; 6,295,467; and 6,415,185; each of which patents is incorporated herein by reference.
The implantable cochlear stimulators described in the U.S. Pat. Nos. 5,626,629; 6,067,474; 6,157,861 and 6,219,580 are also able to selectively control the pulse width of stimulating pulses that are applied through the electrode array to the cochlea, and the frequency at which the stimulating pulses are applied.
The implantable cochlear stimulators described in the U.S. Pat. Nos. 6,157,861 and 6,195,585 teach the use of the stapedius reflex (also referred to as the stapedial reflex) as a parameter for monitoring and adjusting the magnitude of the stimuli applied through the electrode array.
A new generation of cochlear implants, sometimes referred to as “bionic ear” implants, have enhanced processing power, and can provide multiple platforms for delivering electrical stimuli to the auditory nerve. Such electrical stimuli includes high frequency pulsitile stimulation having current pulses of controlled amplitude, width and frequency.
As the art of cochlear stimulation has advanced to produce bionic ear implants, the implanted portion of the cochlear stimulation system, and the externally wearable processor (or speech processor) have become increasingly complicated and sophisticated. It is also noted that much of the circuitry previously employed in the externally wearable processor has been moved to the implanted portion, thereby reducing the amount of information that must be transmitted from the external wearable processor to the implanted portion. The amount of control and discretion exercisable by an audiologist in selecting the modes and methods of operation of the cochlear stimulation system have increased dramatically and it is no longer possible to fully control and customize the operation of the cochlear stimulation system through the use of, for example, switches located on the speech processor. As a result, it has become necessary to utilize an implantable cochlear stimulator fitting system to establish the operating modes and methods of the cochlear stimulation system and then to download such programming into the speech processor. One such fitting system is described in the U.S. Pat. No. 5,626,629. Another fitting system is described in the U.S. Pat. No. 6,289,247.
The U.S. Pat. No. 6,289,247 further highlights representative stimulation strategies that may be employed by a multichannel stimulation system. Such strategies represent the manner or technique in which the stimulation current is applied to the electrodes of an electrode array used with the stimulation system. Such stimulation strategies, all of which apply current pulses to selected electrodes, may be broadly classified as: (1) sequential or non-simultaneous (where only one electrode receives a current pulse at the same time); (2) simultaneous (where substantially all of the electrodes receive current stimuli at the same time, thereby approximating an analog signal); or (3) partially simultaneous pulsitile stimulation (where only a select grouping of the electrodes receive stimuli at the same time in accordance with a predefined pattern).
Typically, when the fitting systems described in the U.S. Pat. No. 5,626,629 or U.S. Pat. No. 6,289,247 are employed for multichannel stimulation systems, or when equivalent or similar fitting systems are employed, it is necessary to use directly measured threshold values and/or thresholds derived from the measurement of psycophysically-determined pseudo-comfort levels. That is, for each channel of the multichannel system, a minimum threshold level is measured, typically referred to as a “T” level, which represents the minium stimulation current which when applied to a given electrode associated with the channel produces a sensed perception of sound at least 50% of the time. In a similar manner, an “M” level is determined for each channel, which represents a stimulation current which when applied to the given electrode produces a sensed perception of sound that is moderately loud, or comfortably loud, but not so loud that the perceived sound is uncomfortable. These “T” and “M” levels are then used by the fitting software in order to properly map sensed sound to stimulation current levels that can be perceived by the patient as sound.
Disadvantageously, determining the “T” and/or “M” levels (or other required thresholds) associated with each channel of a multichannel stimulation system is an extremely painstaking and time-intensive task. Such determinations require significant time commitments on the part of the clinician, as well as the patient. Moreover, once determined one channel at a time, such levels may not be representative of actual threshold levels that are present during real speech. That is, preliminary data indicate that thresholds set in single channel psychophysics overestimate the actual threshold required when all channels are running during live speech. Such an overestimation appears to penalize patient performance, particularly performance in noise. Hence, neural stimulation parameters which render threshold measurement unnecessary would dramatically reduce the time requirements for programming sequential and/or partially simultaneous pulsitile stimulation, as well as facilitate a higher probability of optimized programming for pediatric as well as adult populations where obtaining such measures are difficult.
As the ages of patients into which implantable cochlear stimulators are implanted decreases, it becomes increasingly more important to improve the fitting process and to minimize, or eliminate, the need to make threshold measurements. This is because very young patients, for example, two year olds, are unable to provide adequate subjective feedback to the audiologist for the audiologist to accurately “fit” the cochlear stimulation system optimally for the patient. Thus, what is needed is an improved apparatus and simplified method for fitting a speech processor where many of the threshold measurements previously required are no longer needed, or where subjective feedback from the patient is no longer needed.
One technique that has been investigated for improving the manner in which threshold measurements are made or used is to sense the stapedius reflex of the patient in response to an applied stimulus. See, e.g., the U.S. Pat. Nos. 6,157,861 and 6,195,585, previously incorporated herein by reference. An electrode that may be used to sense the stapedius reflex is described, e.g., in U.S. Pat. No. 6,208,882, also incorporated herein by reference.
When the stapedius reflex is sensed, i.e., when a stapedius reflex electrode is in place that allows the stapedius reflex to be sensed, or when other techniques are used to sense the stapedius reflex, such sensing eliminates or minimizes the need to rely solely upon subjective feedback from the patient during the fitting or adjusting process. Such subjective feedback can be highly unreliable, particularly in younger and older patients.
Traditional methods for measuring stapedial reflexes present stimuli, typically pulse trains, on a single electrode and the reflex is either directly observed by visual inspection or is inferred from a change in the impedance of the tympanic membrane. Advantageously, when compared to other objective measures such as neural responses in the cochlea or brainstem, the stapedial reflex shows the strongest correlation to the patient's comfort level to the stimulus. In spite of this correlation to comfort level, which has primarily utility for the programming of implants in children, there are two major problems that limit is effectiveness as a clinical tool. These problems are: (1) approximately 20–30% of patients do not provide an easily measured stapedial reflex, and (2) single electrode measurements fail to account for temporal and spatial integration, and thus such single electrode measurements likewise fail to account for the actual comfort level settings for the stimulus during multi-electrode activation, as occurs during “live speech”.
It is thus seen that improvements are still needed in the manner in which the stapedial reflex is obtained and used during the fitting and operation of a cochlear implant system.